Spent sulfuric acid is generated in several petroleum processes including alkylation of olefinic hydrocarbons with isoparaffins and nitration of aromatics. The production of motor alkylate is still a major process in many refineries. Without regard to the particular petroleum process that is the source of spent sulfuric acid, such spent acid will typically result in dilution of acid due to the formation of acid soluble oils.
The recovery of sulfuric acid from such acid soluble oils is an economic factor for the recycling of spent acid. Spent acids can be recovered by methods such as combustion, distillation, evaporation, stripping spent acid with a stripping gas, or extraction but they are not efficient due to the strong interaction between the acid and oil. More recent methods have used hydrogenation of acid soluble oils to recover spend acid.
Because of the expense involved in on-site regeneration of spent sulfuric acid, many refiners send spent acid off-site for acid recovery. However, this entails significant handling and transportation costs which adds to the cost of spent acid regeneration.
There is a need for a cost-effective means of integrating sulfuric acid recovery into petroleum processes which involve acid treatment of hydrocarbons.